Yesterday, Mitchell issued a brief statement: "It may be easy for people who were not there and didn't feel the pressure of the threats to say how much better they could have done it. But they weren't there. We were and we did the best that we could."

The 'Manchester Manual'

A silver-maned, voluble man, Mitchell had retired from the Air Force before the Sept. 11 attacks and won several government contracts, including one from the CIA to study ways to assess people who volunteered information to the agency. While still in the military training program known as SERE -- for Survival, Evasion, Resistance, Escape -- he and his colleagues called themselves "Masters of the Mind [Expletive]," according to two military officials who worked in the program.

In December 2001, the CIA asked Mitchell to analyze the "Manchester Manual," a document seized in a raid in Britain that described al-Qaeda resistance techniques. Mitchell asked Jessen, a senior SERE psychologist, to help prepare the assessment, according to Senate investigators.

The Mitchell-Jessen memo, which was distributed widely within the CIA, discussed the efficacy of techniques such as sleep deprivation and noise bombardment but did not broach waterboarding.

"It is not realistic to think someone who is hardened will talk unless they fear that something bad is going to happen to them," said the former U.S. official, describing Mitchell and Jessen's thinking. "They didn't think rapport-building techniques would work. But they also didn't [advocate] using waterboarding right away."

Mitchell told acquaintances that he also drew important lessons from the theory of "learned helplessness," a term psychologists use to describe people or animals reduced to a state of complete helplessness by some form of coercion or pain, such as electric shock. Mitchell insisted, however, that coercive interrogation should not reduce a prisoner to despair. Instead, he argued, "you want them to have the view that something they could say would hold the key to getting them out of the situation they were in," according to the former official.

"If you convince [a terrorism suspect] he's helpless, he's no good to you," the former official said.

A Breakthrough in Bangkok

In early April 2002, some officials at the CIA's Counterterrorist Center were not convinced that the man in U.S. custody was indeed Zayn al-Abidin Muhammed Hussein, Abu Zubaida's given name. The Saudi-born Palestinian, then 29, had been sought by the FBI on suspicion that he played a role in a foiled 1999 plan to attack Los Angeles International Airport and tourist destinations in Jordan.

The detainee had been captured in Pakistan in late March 2002 after a firefight that left him wounded in the thigh, groin and stomach. After being treated in Pakistan, he was flown to Thailand for interrogation.

The CIA dispatched FBI agents Ali Soufan and Steve Gaudin for an initial look. The two men arrived a few hours before the wounded man was transferred to a hastily assembled CIA interrogation facility near one of Bangkok's airports.

Details of their experience and that of the CIA officials who followed them to Thailand with Mitchell were gleaned from public testimony, official documents and interviews with current and former intelligence and law-enforcement officials with access to confidential files. Through the FBI, Gaudin declined to comment for this article, and Soufan referred reporters to his congressional testimony and other public statements.

Soufan, a Lebanese American, later described the FBI's method as "informed interrogation." It was based on "leveraging our knowledge of the detainee's culture and mind-set, together with using information we already know about him," he told a Senate panel in May.